1. Field of the Invention
The present invention relates to a memory system. For example, the present invention relates to a memory system having a nonvolatile semiconductor memory that allows data to be rewritten and a controller that controls the nonvolatile semiconductor memory.
2. Description of the Related Art
Memory cards using nonvolatile semiconductor memories, for example, flash memories, are used as recording media for music data and video data. A typical example of a flash memory for a memory card is a NAND flash memory.
Some memory cards comprise a single card in which a NAND flash memory and a controller that controls the NAND flash memory are mounted. This controller is hereinafter referred to as a card controller (or memory controller). To reduce current consumption, the memory card avoids connecting a pull-up resistor to an I/O line (data line) that connects the card controller and the NAND flash memory together. The card controller controls the I/O line so that data can be written to or read from the NAND flash memory without the need to connect the pull-up resistor to the I/O line. For example, the card controller outputs data to the I/O line for a write operation and allow the I/O line to float for a read operation.
The current NAND flash memory outputs data in a serial read mode. Thus, the card controller controls timings for the I/O line in a manner compatible with the serial read mode.
Some recent host instruments using a memory card as a recording medium require an enormous amount of data to be recorded in the card. Thus, the NAND flash memory has been requested to support a high-speed read mode in which data is read faster than in the serial read mode. In the high-speed read mode, for example, accesses are made to the NAND flash memory at reduced intervals. In this case, the timing control for the I/O line by the card controller is different from that in the serial read mode. This results in the need for many types of memory cards corresponding to the read modes. This situation is inconvenient for users.